1. Field of the Invention
The present invention relates, in general, to a charger in which a plurality of charging modules, each capable of independently and performing a complete charging operation, is connected in parallel, and which can charge a battery without being limited by the capacity of the battery, and, more particularly, to a charger capable of performing the integrated control and separate control of parallel operations, which can simultaneously operate all charging modules without performing signal transmission between respective charging modules, thus eliminating the risk of overcharging or insufficient charging that may occur when a plurality of charging modules is connected in parallel in order to charge a battery.
2. Description of the Related Art
Generally, since a charger is set according to the capacity of a battery to be charged, it is impossible to charge batteries having other capacities using the set charger. Therefore, companies for manufacturing chargers must produce various types of chargers for respective battery capacities. In particular, since large-capacity chargers having a current of more than several hundreds of Amperes are expensive pieces of equipment at prices of even several million Won, they are problematic in that there is a large burden of stored goods, and it is difficult to meet the time for payment due to the difficulty of the manufacture, and in that the entire expensive charger must be replaced when a failure occurs in such a charger, so that a loss caused by the replacement is large, and thus it is difficult for medium and small-sized enterprises to attempt to manufacture such an expensive charger.
Therefore, there is a need to solve the above problems by providing a charger in which charging modules, each capable of independently performing a complete charging function as a single independent charger, are connected in parallel, and which can be used without being limited by the capacity of a battery (that is, may be used as a large-capacity charger).
However, when several charging modules are connected in parallel, it is difficult to simultaneously operate the charging modules as in the case of a single charger, thus resulting in several problems. The reason for this will be described below.
FIG. 1A is a diagram showing the typical charging profile of a charger for charging a lead-acid battery. The charger sequentially supplies charging power, corresponding to a primary constant current, a constant voltage and a secondary constant current, to the battery, thus charging the battery.
The constant current supplied during the primary constant current period T0˜T1 is set in a range of from 10 to 15% of the capacity of the battery. During this period, about 70 to 80% of the discharging amount of the battery is charged.
During a constant voltage period T1˜T2, when the charging level of the battery reaches a predetermined level (the start time point of the constant voltage period), the generation of gas from the battery is started, and thus current is reduced while the voltage is maintained at a constant value.
During a secondary constant current period T2˜T3, the constant current is set in a range of from 2 to 4% of the battery capacity. During this period, about 110% of the discharging amount of the battery is charged.
When several chargers (charging modules), each being a wholly independent charger having such a charging profile (a primary constant current, a constant voltage, and a secondary constant current) are connected in parallel, and then a large-capacity battery is intended to be charged, charging is not successfully performed as if a single charger had been operated, due to the following problems below.
A plurality of parallel-connected charging modules has constant voltages set to the same voltage in the constant voltage period, but has a certain error due to each individual charging module's own peculiar characteristics (for example: precision of detection of output voltage). That is, respective charging modules are different from each other in the start time point and end time point (start time point of the secondary constant current period) of the constant voltage period. In particular, the time point at which the secondary constant current period starts after the constant voltage period has been terminated is the time point at which a timer counts a time to terminate the charging operation of each charging module, and thus it is a very important point in time.
In this way, when the time points at which respective charging modules reach the secondary constant current are different from each other due to the error of the constant voltage, the time points at which the charging operations of respective charging modules are completed are also different from each other. Furthermore, as shown in FIG. 1B, a specific charging module may enter the state in which variation in voltage dV/dT is not detected due to the error in which an output voltage is not changed even if the charging level of the charging module has reached a secondary constant current (since charging modules are connected in parallel, the output voltages thereof are equal to each other), thus making it impossible to perform normal charging.
In addition, when, during the secondary constant current period, a specific charging module succeeds in detecting variation in voltage dV/dT, and then completes charging earlier than other charging modules, the current of the module, having completed the charging, is subtracted from the total current supplied to the battery, and thus the voltage of the battery rapidly decreases. As a result, other modules, which do not yet detect variation in voltage dV/dT, cannot detect correct variation in voltage dV/dT, and a procedure for detecting the voltage variation dV/dT again from the time point at which the voltage decreases must be repeated, thus causing the risk of overcharging.
Further, the secondary constant current value is set in a recommended range for each manufacturing company in consideration of the internal characteristics and overcharging or insufficient charging characteristics of a battery. At this time, when a plurality of charging modules is connected in parallel, and the sum of currents, output from respective charging modules, becomes the charging current of the battery, a constant current supplied to the battery is less than a preset charging constant current when a failure occurs in some charging modules, thus increasing a charging time. When charging is compulsorily terminated using a timer, there is a problem in that the battery may be insufficiently charged due to such early termination of charging.
As described above, problems, occurring when the plurality of charging modules is connected in parallel to charge a battery, are compositely generated regardless of the sequence of the problems, so that there is a fear that overcharging and insufficient charging, negatively influencing the lifespan of a battery, are repeated. Further, since the charging operations of charging modules are not terminated at the same time, there is a probability that a user may confuse the completion of charging.